Graff took a seven-day cruise last fall on the Carnival Fantasy to Grand Turk, Half Moon Cay and Nassau, Bahamas and had a wonderful time. "It was a fantastic trip," wrote Graff, a photographer in Fuquay-Varina, North Carolina, in an email.

"A few veteran cruisers grumbled about the age of the ship, and the decor being dated, but the service and experience was really great," he said.

Graff said he would definitely take another Carnival cruise. But he has some conditions.

"There's no question that Carnival should be seriously looking into their maintenance policies and double-checking their work to make sure their customers and crews are having the safest voyages possible," wrote Graff. "If these issues continue to go on unchecked, then I'll change my answer."

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Carnival hits more choppy waters

Carnival has a window of opportunity to convince customers its ships can sail without too much trouble, according to several travel agents and cruisers interviewed by CNN.com. But the company has to prove it is tackling the recent spate of mechanical issues faced by four Carnival ships, the most serious of which left more than 4,000 people stranded for days aboard the Carnival Triumph last month.

'A grace period' to fix things

Carnival has a grace period of a couple months to get its act together, according to travel agent Ricci Zukerman. Her mostly high-end clients occasionally book a more budget-oriented Carnival cruise for a family reunion or when they're bringing teenagers along because "they're the fun ships," she said.

"Carnival has been in business for many years, and for a long time there's never been a hitch," said Zukerman, president of Worldview Travel. But they need to attend to their maintenance issues. "If it happens again, I think people will start worrying. There are other ships in the ocean," although none quite so affordable, she said.

Carnival Cruise Lines announced a "comprehensive review" this week of all its ships, prompted by the engine fire that led to the Triumph's stranding in the Gulf of Mexico in February.

As the biggest cruise company in the world, parent company Carnival Corp. has a strong reputation in the industry and among its regular customers, said Kimberly Wilson Wetty, co-president of Valerie Wilson Travel.

In addition to Carnival Cruise Lines, the corporation's portfolio includes brands such as Holland America Line, Princess Cruises, Seabourn, Cunard and Costa Cruises. The Costa Concordia had a deadly accident off the coast of Italy last year.

Total advance bookings across all of Carnival Corp.'s brands for 2013 are behind 2012 levels, Carnival said in a news release Friday announcing first quarter financial results. But despite the overall lag, booking volume since January for the rest of the year has been "running significantly higher than last year at slightly higher prices," the company said.

"Despite considerable attention surrounding the Carnival Triumph, we had been encouraged to see booking volumes for Carnival Cruise Lines recover significantly in recent weeks," said Micky Arison, chief executive officer of Carnival Corp.

"All ships experience some challenges," said Wetty, who traditionally books her customers on high-end cruises. "It's all the recovery and how they treat the passengers and how they continue to build consumer confidence.

"For those who are consistent cruisers and know Carnival, I don't think it's going to change their buying habits. For new cruisers, it puts a little doubt in their minds. "

Not every frequent Carnival cruiser is feeling so confident.

"I have cruised with Carnival on many occasions with my family. They were my [favorite] cruise line. That being said, I will stay on land from here on out," wrote one CNN.com commenter.

"Until they have a really really long period of time with no problems I will not consider cruising with them again. This is just way too much. The Concordia going down was bad enough, but all of these are just plain nonsense. It WILL hurt the cruise line."

Customers need to be reassured Carnival is doing everything it can to address its ships' issues, Wetty said.

Current customers, some of whom have been posting on CNN.com, are having trouble reaching the company in some cases.

"What about those of us that got our cruise canceled?" wrote one commenter, who said she was scheduled to sail on the Carnival Dream. "I haven't heard anything from Carnival, and I don't know how long it will take to get a refund. Now we are stuck not knowing what to do for a vacation we saved 8 years to take!"

Still, Connie Hammond is one of those Carnival fans who isn't giving up on the cruise line.

"All three of my prior Carnival cruises were wonderful, food was outstanding, ports were well organized and safe, shipboard activities were plentiful, all for a small budget price," Hammond, a resident of Fort Madison, Iowa, wrote in an e-mail.

"I'm sure I could have paid $1,000 more per person and been impressed much more, but the Carnival cruise was a great vacation and a memorable fun time."

Hammond said she expects the recent incidents will be a wake-up call for Carnival's maintenance program, but she's not concerned about safety.

She's already booked her next Carnival cruise, taking her 79-year-old mother and a girlfriend who has never been on a cruise.

Days of sipping umbrella drinks have given way to the stench of backed-up sewage, stuffy cabins without power and limited food. The Carnival Triumph engine fire shows that the best-laid cruise plans can veer terribly off course.